feat(claude-binary): implement robust version selector with enhanced binary detection

This commit provides a comprehensive solution to Claude binary detection issues
by implementing a user-friendly version selector UI and improving the binary
discovery logic. It addresses all concerns raised in multiple PRs and comments.

Changes:
- Add ClaudeVersionSelector component for selecting from multiple installations
- Update ClaudeBinaryDialog to use version selector instead of manual path input
- Fix unused variable warning in production builds (claude.rs:442)
- Improve select_best_installation to handle production build restrictions
- Add listClaudeInstallations API endpoint to fetch all available installations
- Make Claude version indicator clickable to navigate to Settings
- Move Claude installation selector to General tab in Settings (per user request)
- Enhance dialog UX with loading states and clear installation instructions
- Add Radix UI radio-group dependency for version selector

Fixes:
- Production build warning about unused claude_path variable
- Version detection failures in production builds due to process restrictions
- Poor UX when Claude binary is not found (now shows helpful dialog)
- Inability to easily switch between multiple Claude installations

This implementation takes inspiration from:
- PR #3: Version selector dropdown approach (preferred by users)
- PR #4: Binary detection improvements and path validation
- PR #39: Additional detection methods and error handling
- Commit 5a29f9a: Shared claude binary detection module architecture

Addresses feedback from:
- getAsterisk/claudia#4 (comment): User preference for dropdown selector
- Production build restrictions that prevent version detection
- Need for better error handling when Claude is not installed

The solution provides a seamless experience whether Claude is installed via:
- npm/yarn/bun global installation
- nvm-managed Node.js versions
- Homebrew on macOS
- System-wide installation
- Local user installation (~/.local/bin, etc.)

Refs: #3, #4, #39, 5a29f9a

src/components/AgentExecution.tsx

@@ -70,7 +70,7 @@ export const AgentExecution: React.FC<AgentExecutionProps> = ({
   className,
 }) => {
   const [projectPath, setProjectPath] = useState("");
-  const [task, setTask] = useState("");
+  const [task, setTask] = useState(agent.default_task || "");
   const [model, setModel] = useState(agent.model || "sonnet");
   const [isRunning, setIsRunning] = useState(false);
   const [messages, setMessages] = useState<ClaudeStreamMessage[]>([]);
@@ -646,7 +646,7 @@ export const AgentExecution: React.FC<AgentExecutionProps> = ({
                 <Input
                   value={task}
                   onChange={(e) => setTask(e.target.value)}
-                  placeholder={agent.default_task || "Enter the task for the agent"}
+                  placeholder="Enter the task for the agent"
                   disabled={isRunning}
                   className="flex-1"
                   onKeyPress={(e) => {